Shortly after I bought it I had both motor mounts and tranny mounts replaced. The fuel primer pump was leaking diesel fuel all over the rubber mounts and deteriorated them completely. I replaced that myself. Since the engine was not properly in place one of the belts wore a notch into my oil cooler return hose and spewed oil all over my engine bay and driveway. I had the upper and lower hoses replaced at the same time as the mounts. ($1300)
I've personally replaced many various vacuum lines/fittings, boost sensor, glow plugs, cleaned the banjo-bolt and ALDA lines from the intake manifold, installed the European headlights (one-piece glass) and installed a Pioneer CD player w/iPod cable.
All in all none of these things were too difficult, just requires some time and patience to do the job the right way. I'm tackling new brake rotors/calipers/pads once they all arrive. Though, most of this is just general maintenance that needs to be done. If you buy a car with an OM617 (3.0, 5-cyl turbo) take it to your dealer right away and have them do a valve adjustment. ($170) These engines require valve adjustments every 10k-15k. I just had mine done (after putting almost 11k on it and what a difference!) This was fixed on the later 6-cyl turbo models by using a hydraulic valve-train, though, those engines are prone to cracked heads.
The OM617 is possibly the greatest engine MB ever designed. Take care of it and it will last longer than you.
I've gotten numerous parts from my local dealership who is always very prompt and I don't mind paying a little extra for that MB quality and service.
Excellent build quality/fit and finish. My seats are cracked and torn, it kinda smells inside, my wood is cracked and chipping, but the car starts the first time, every time. The doors close like a bank vault (you know it when you hear it). You feel like king of the road, even though the car is 22 years old!
I've driven from Shreveport, La. to KC, Mo. on one tank of gas! It averages about 27mpg, and for such a large, heavy, old car that isn't too bad! I don't feel bad putting any amount of miles on my car, or driving it anywhere. I'd take it across country tomorrow if I had too!
I'm actually looking forward to the high mileage for the award and grille badges MB provides.
I bought it from the original owner, who used it as a daily driver/beater and only took care of the mechanical things. I have all of the original paperwork including the window sticker and every repair documented. I was very lucky to find such a meticulous previous owner.
The car handles well, especially with the aging bushings and bearings that surely need replacing. You can go for a long time in the car without feeling sore or fatigued. I suppose it was designed that way.
I don't mind that my car isn't perfect because it gives me the chance to do some resto-work myself and really make it my own. Plus its fun and rewarding.
Though, I was lucky, I wouldn't recommend jumping on the first deal that comes your way. Have the car checked out by a mechanic who knows Mercedes vehicles.
There is a saying around the forums that I visit; "Theres nothing more expensive than a cheap Mercedes!"
Best of Luck!